The present invention generally relates to integrator circuits and more particularly to the use of low leakage integrator circuits in a carburetor control system.
Integrators using an operational amplifier having a capacitor coupled between the output and inverting input terminals of the amplifier and receiving an input signal at the inverting input terminal through a resistor are well known in the prior art. Such integrators are known to produce an output voltage related to the time integral of the input voltage with respect to a reference voltage received at the non-inverting input terminal of the operational amplifier. When no voltage is applied to the inverting input terminal of the operational amplifier, then this terminal will remain at a voltage equal to the reference voltage plus an input offset voltage, and the output terminal of the operational amplifier will retain the voltage it had prior to the removal of the input voltage which had been applied to the inverting terminal. Generally, a pair of controllable gates is connected across the feedback capacitor so as to discharge this capacitor in order to reset the operational amplifier integrator.
In order to implement an integrate and hold circuit, the above operational amplifier can be combined with a series gate that selectively interrupts the application of an input voltage to the inverting input terminal of the operational amplifier. However, such gates do have finite resistances and leakages and due to their combined effect such an integrate and hold circuit would have output drift problems since during the hold mode a leakage input signal would continue to charge the feedback capacitor through the controllable series gate. While the prior art has recognized the problem caused by the leakage through a series input gate, only complex and costly solutions to this problem have been proposed. The present invention provides an inexpensive and simplified solution to the problem and also illustrates how such a low leakage integrator circuit can be utilized in a carburetor control system.